The present invention relates to a method and an apparatus for monitoring a three-dimensional spatial area. More particularly, the invention relates to a method and an apparatus designed for safeguarding an automatically operating installation which poses a risk to persons or other objects. By way of example, the automatically operating installation can be a robot whose movements constitute a risk for persons or objects that are present in the working envelope of the robot. The classical approach is to protect such automatically operating installations by means of mechanical blocking means such as protective fences, protective doors and the like, and by means of light barriers and/or laser scanners. The working envelope of the installation is blocked such that the intrusion of a person or another foreign object is prevented or at least detected. In the last case, detection leads to a shutdown of the installation and/or to another safety reaction.
Light barriers, laser scanners and protective fences, however, can block an automatically operating installation only over a relatively large space and with rigid, largely rectilinear boundary surfaces. Such blocking thus requires a relatively large space and is inflexible and complicated to install. Moreover, such blocking means can substantially impair the operability of the installation, and this frequently leads to manipulations and risks of accidents resulting therefrom.
For this reason, there have been efforts for some time to safeguard dangerous working envelopes of automatically operating installations by means of camera-based monitoring apparatuses. WO 2004/029502 A1 discloses such an apparatus. The known apparatus has three image recording units of which each two image recording units form a pair. Recorded image pairs are evaluated by means of two algorithmically different methods in order to obtain three-dimensional image data of the monitored spatial area. These image data can be used to monitor virtual protection zones around the monitored installation. The known apparatus, however, is not yet optimal, because it requires a relatively large minimum distance between the image recording units and the monitored spatial area.
DE 100 49 366 A1 discloses another method and apparatus for monitoring a spatial area by means of at least a first and a second image recording unit whose viewing areas are oriented in at least partially overlapping fashion. A virtual protection zone is monitored within the common viewing area. The use of at least two image recording units serves the purpose here of detecting disturbing factors in the near zone such as, for example, an insect that runs over the lens of one of the image recording units, in order to avoid a false alarm being triggered for that reason. Consequently, the apparatus of DE 100 49 366 A1 triggers an alarm signal only when a foreign object is simultaneously detected and classified as being relevant to an alarm by both image recording units. In addition, a three-dimensional evaluation of the recorded images is envisaged in order to further reduce disturbing influences in the case of the detection of alarm-relevant objects, for example by detecting only objects in a defined distance range. However, the known method and apparatus are not suitable for safeguarding the working envelope of an automatically operating installation with a sufficient error tolerance.